Biodegradable high-molecular polymers, production and use thereof

Abstract

The invention provides a method of purifying biodegradable aliphatic polyesters which comprises dissolving, in a readily water-soluble organic solvent, a biodegradable aliphatic polyester which contains low-molecular substances and adding water to the resulting solution to thereby remove said low-molecular substances, biodegradable aliphatic polyesters obtained by said method and containing low-molecular substances with a molecular weight of 1,000 or less in an amount of not higher than 3%, and drug-containing compositions which comprise any of said biodegradable polyesters.

What is claimed is: 
     
       1. A method of purifying a biodegradable aliphatic polyester produced without using a catalyst and separated out and collected after polymerization reaction, comprising about 50 to 100 mole percent of lactic acid and about 50 to 0 mole percent of glycolic acid, having a weight average molecular weight of about 3,000 to 50,000 as determined by gel permeation chromatography with a polystyrene standard and containing oligomers having a molecular weight up to 1,000 as determined by gel permeation chromatography with a polystyrene standard, said method comprising: (a) dissolving, in 100 parts by volume of a water-soluble organic solvent, a crude biodegradable aliphatic polyester which contains said oligomers to produce a solution,   (b) gradually adding 50 to 150 parts by volume of water to the solution with stirring,   (c) recovering a resulting precipitate or oil layer, and   (d) washing the recovered precipitate or oil layer with water to obtain a purified biodegradable aliphatic polyester containing equal to or less than 3% by weight of oligomers.   
     
     
       2. The method according to claim 1, wherein both lactic acid and glycolic acid are present in the biodegradable aliphatic polyester. 
     
     
       3. The method according to claim 1, wherein the water-soluble organic solvent is a member selected from the group consisting of acetone, tetrahydrofuran, dioxane, dimethylformamide and dimethylsulfoxide. 
     
     
       4. The method according to claim 3, wherein the readily water-soluble organic solvent is acetone.